No. I.] SENSE-ORGANS OF LUMBRICUS AGRICOLA. 223 



correspond to Lenhossek's descriptions and illustrations of the 

 nerve-cells, but I have found them to be in every case in one 

 of the sense-organs seen by previous observers. It is my 

 opinion that the isolated nerve-cells described by Lenhossek 

 are the sense-cells of the sense-organs. It will be noticed 

 that his diagram of the appearance of these cells in the epi- 

 dermis (see Lenhossek, '92, Taf. V, Fig. 6) represents a section 

 through the region of the setae, the very region in which 

 the sense-organs are most numerous, and that he more often 

 figures these cells in groups of two or three than isolated. 

 Lenhossek's illustrations and descriptions of these " Nerven- 

 zellen " correspond exactly to the sense-cells of the sense-organs 

 as they appear in my silver nitrate sections, except that I have 

 never found the basal processes of these cells running as far 

 along the base of the epidermis as he figures them. It seems 

 to me not unlikely that some of the long ends of these 

 processes may be parts of the subepidermal network. That 

 Lenhossek failed to recognize these organs may be due to the 

 fact that the silver stains but few of the cells of one organ. 

 And if he used thick sections mounted without a cover-glass, it 

 would probably be impossible to perceive the unstained sense- 

 cells and the outline of the sense-organ. 



Lenhossek figures his nerve-cells as ending at the cuticula. 

 The difficulty of retaining the cuticula in position and the 

 heavy deposit of silver made along it, seems to me to explain 

 his failure to find the sense-hairs. In all my sections in which 

 the sense-cells were stained, the sense-hairs were almost or 

 quite withdrawn, and might therefore be readily overlooked. 

 My own experience has shown me that a knowledge of the 

 structure of the sense-organ as shown in haematoxylin prepara- 

 tions is necessary for a correct interpretation of the appearance 

 obtained by the silver nitrate method. Lenhossek stated that 

 in haematoxylin preparations his nerve-cells could scarcely be 

 told from the supporting cells; I have found that the sense- 

 cells of the sense-organs may be readily distinguished from the 

 supporting cells in all my preparations. 



Retzius ('92a) figures and describes the isolated nerve-cells 

 of Lenhossek. He figures at the base of the epidermis a net- 



